What is the best visa option for traveling in Thailand for over a year?

It depends if you have the funds needed in your bank acct get the 6-month METV visa. Every 60 days you have to make a border bounce either by air or land or pay 1,900 THB at immigration for a 30-day extension. Tthe total time you can get out of it is 270 days [6-month METV costs $200 or equivalent]....Pro Tip to get the 270 days do a border bounce before the expiration date of the visa so that will give you an extra 60 days.

The 6 Month METV can only be issued in your home country, a country you are a Permanent Resident, or in Australia if your passport is on their list of countries.

The 60-day SETV that you can extend at immigration for 30 days at 1,900 THB to give you a total of 90 days in the country....These are easily obtained in your home country and at Thai Embassies and Consulates worldwide.

If you want an extended stay visa to get an Ed Visa where you have to do the minimum time for learning in the subject that you choose....Ed Visas range from 25,000THB to 45,000THB for a year-long course. The course will give you 3, 90-day extensions which you will have to go the immigration office to apply for and do your 90-day report.

If you older than 50 you can apply for a Non Immigrant O-A visa in your home country, If you are married to a Thai National you can apply for a Non Immigrant O visa based on marriage. Otherwise you can apply for the Multiple Entry Tourist Visa in your home country, when good used you get 270 days out of this visa. Most Embassy/Consulate has the same speed, apply day nr 1, pick up next working day.